Lean-fuel gas turbine engine

ABSTRACT

Provided is a compact lean-fuel gas turbine engine which does not cause performance degradation of the engine or pressure loss in the exhaust system, which comprises a compressor ( 1 ) for compressing an operative gas (G 1 ) to generate a compressed gas (G 2 ), the operative gas (G 1 ) having a concentration of burnable component which is less than a flammability limit thereof, a catalytic combustor ( 2 ) for combusting the compressed gas (G 2 ) by a catalytic reaction with an aid of a catalyst accommodated therein to generate a combustion gas (G 3 ), a turbine ( 3 ) adapted to be driven by the combustion gas (G 3 ) supplied from the catalytic combustor ( 2 ), a regenerator ( 6 ) for heating the compressed gas (G 2 ) supplied from the compressor ( 1 ) to the catalytic combustor ( 2 ) by an exhaust gas (G 4 ) supplied from the turbine ( 3 ) through an exhaust gas passage ( 25 ) to the regenerator ( 6 ), a burner ( 7 ) for burning a gas (G 20 ) extracted from the compressor ( 1 ) with a fuel to generate a heating gas (G 5 ) and supplying the heating gas (G 5 ) into the exhaust gas passage ( 25 ) and a valve ( 8 ) for controlling an amount of the extracted gas (G 20 ) to be supplied to the burner ( 7 ).

TECHNICAL FIELD

The present invention relates to a lean-fuel gas turbine engine which uses low BTU gas fuel such as Coal Mine Methane (CMM) extracted from coal mines or landfill gas created in the landfill.

BACKGROUND OF THE INVENTION

Conventionally, there has been known a lean-fuel gas turbine engine which intakes low BTU gas with a methane concentration lower than its flammability limit to combust the methane component. According to the gas turbine engine, an operative gas with low concentration methane is compressed by the compressor to generate a compressed gas. The compressed gas is combusted by a catalytic combustor through catalytic reaction to generate combustion gas. The combustion gas is then used to drive a turbine. The compressed gas discharged from the turbine is then transported into a regenerator or heat exchanger where it is used for preheating the compressed gas being transported from the compressor to the catalytic combustor. A duct burner is provided in a discharge gas passage connecting between the outlet of the turbine and the inlet of the generator where fuel such as natural gas is introduced and then combusted at start-up or low-load operation in which the discharge gas has low temperature. This increases a temperature of discharge gas to sufficiently heat the compressed gas to be fed from the compressor into the regenerator and, as a result, to activate the catalytic combustor and thereby drive the engine in an effective manner. See JP 2010-19247 (A).

The gas turbine engine is capable of using VAM (Ventilation Air Methane) of low BTU gas with low concentration methane, discharged from coal mines. The VAM has a methane concentration of only 1% or less. Therefore, conventionally the VAM is discharged into the air without being combusted. However, the use of the VAM as fuel for generation of electric power by the gas turbine will acquire a certain amount of carbon dioxide emission rights.

The above-described gas turbine engine, because the duct burner is mounted within the exhaust passage at the turbine outlet, causes pressure loss and output decrease of the engine due to the exhaust gas running through the passage from the turbine even in rated operations in which the duct burner is turned off. Also, a flow rate of the combustion air to the duct burner is unable to be controlled, which makes it difficult to re-ignite the duct burner in conditions where the catalytic in the catalytic combustor is deteriorated. Further, because the duct burner is mounted within the exhaust gas passage, the passage and the resultant gas turbine should be large-scaled.

An object of the present invention is to provide a lean-fuel gas turbine engine without causing any decrease in the output power of the engine or any pressure loss in the exhaust system, which results in a small size gas turbine.

SUMMARY OF THE INVENTION

To this end, the lean-gas turbine engine comprises a compressor for compressing an operative gas to generate a compressed gas, the operative gas having a concentration of burnable component which is less than a flammability limit thereof; a catalytic combustor for combusting the compressed gas by a catalytic reaction with an aid of a catalyst accommodated therein to generate a combustion gas; a turbine adapted to be driven by the combustion gas supplied from the catalytic combustor; a regenerator for heating the compressed gas supplied from the compressor to the catalytic combustor by an exhaust gas supplied from the turbine through an exhaust gas passage to the regenerator; a burner for burning a gas extracted from the compressor with a fuel to generate a heating gas and supplying the heating gas into the exhaust gas passage; and a valve for controlling an amount of the extracted gas to be supplied to the burner.

According to the gas turbine engine, the operative with a concentration of burnable component less than a flammability limit thereof is compressed by the compressor to generate the compressed gas. The compressed gas is combusted through the catalytic reaction in the catalytic combustor to generate the high-temperature combustion gas which is used for the driving of the turbine. When the inlet temperature of the catalytic combustor is less than a temperature necessary for initiating the catalytic reaction, for example, during the starting or low-load operation, the heating burner generates the heating gas by burning a mixture of the fuel and the gas extracted from the compressor, which is supplied into the exhaust gas passage to heat the exhaust gas. The heated exhaust gas is then heat-exchanged with the compressed gas from the compressor at the generator. The heated compressed air increases the inlet temperature of the catalytic combustor to activate the catalytic combustion, which ensures a stable supply of the high-temperature combustion gas to the turbine. Also, the heating burner is provided outside the exhaust passage, which results in no pressure decrease in the exhausting system or no performance degradation of the engine. Further, the usage of the lean gas such as CMM, VAM or landfill gas with lower fuel concentration or methane concentration for driving the gas turbine engine or the usage of the catalytic reaction does not generate NOx in the rated operation in which the burner is not activated and ensures a reduction of the methane gas emission to contribute the prevention of global warming.

In addition, the heating burner is not provided in the exhaust gas passage, which does not cause any pressure loss in the exhaust system or performance degradation of the engine and therefore ensures an efficient operation of the engine. Also, no heating burner is provided in the exhaust passage, which does not result in any enlargement of the passage or the gas turbine engine. Further, the extraction valve controls the amount of extracted gas to the heating burner, which ensures a suitable control of the extracted gas in the re-ignition of the burner to generate a certain amount of heating gas required by the burner. This facilitates the ignition of the burner.

In a preferred embodiment, the extraction valve is adapted to continuously increase or decrease the amount of the extracted gas to be supplied to the heating burner. According to this embodiment, an amount of extracted gas to be supplied to the heating burner is continuously controlled by the extraction valve. This ensures that the amounts of extracted gas and the fuel to be supplied to the heating burner and, as a result, the flow rate and the temperature of the heating gas from the burner are controlled in a reliable manner. This enables the inlet temperature of the catalytic combustor to be controlled in a stable manner.

In another preferred embodiment, the heating burner is activated in a start-up operation of the gas turbine engine. According to the embodiment, the heating burner is operated in the start-up operation of the engine to activate the catalytic combustor and then drive the engine smoothly, although in the conventional start-up operation the temperature of the exhaust gas from the turbine is still low and therefore the catalytic combustor is not activated to the extent necessary for supplying the high-pressure and high-temperature compressed gas into the turbine and thereby increasing the rotation number of the engine.

In another preferred embodiment, the heating burner works in a condition where the gas turbine engine works under the non-rated operation of which a rotation number is less than that of a rated operation of the gas turbine engine. According to the embodiment, the total amount of the operative gas passing through the gas turbine engine in the non-rated operation is less than that in the rated operation. This means that the heating burner requires less amount of fuel, which allows that a smaller heating burner is used for the engine.

In another preferred embodiment, the gas turbine engine is adapted so that the heating burner works when a combustion failure occurs at the catalytic combustor. According to the embodiment, even when any combustion failure occurs due to a deterioration of the catalyst, the heating burner can be re-ignited to activate the catalytic combustor and thereby prevent a performance reduction of the engine.

In conclusion, the gas turbine engine can be activated by the lean gas having a lower fuel concentration, for example, methane concentration. Also, the catalytic reaction does not generate NOx in the rated operation and also reduces methane gas emission. Further, because the heating burner is not provided in the exhaust gas passage, a smaller exhaust gas can be used to reduce the size of the gas turbine engine. In addition, this structure results in no pressure loss in the exhaust gas passage or no performance degradation of the engine.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a structure of a lean-gas gas turbine engine according to an embodiment of the invention;

FIG. 2 is a diagram showing a featured structure of the gas turbine engine according to the embodiment of the invention; and

FIG. 3 is a time chart showing a start/stop operation of the gas turbine engine according to the embodiment of the invention.

PREFERRED EMBODIMENT OF THE INVENTION

With reference to the accompanying drawings, a preferred embodiment according to the invention will be described below. FIG. 1 is a schematic diagram showing a structure of a lean-fuel gas turbine according to the embodiment of the invention, in which a gas turbine generally indicated by GT has a compressor 1, a catalytic combustor 2 containing catalyst such as platinum or palladium and a rotating machine 4 which uses output of the gas turbine GT to work as an electric generator or a starter.

The gas turbine uses operative gas G1 which is a mixture of air and fuel. The operative gas may be low BTU gas such as Ventilation Air Methane (VAM) generated in coal mines or Coal Mine Methane (CMM) of which a concentration of burnable component (methane) is greater than that of VAM, extracted from coal mines or landfill gas created in the landfill. The operative gas G1 is compressed by the compressor 1 to generate a high-pressure compressed gas G2 which is transported to the catalytic combustor 2 where it is combusted through catalytic reaction with an aid of catalyst such as platinum or palladium to generate a high-temperature and high-pressure combustion gas G3. The combustion gas G3 is supplied to the turbine 3 to drive the turbine. The turbine 3 is connected to the compressor 1 through a rotating shaft 5 so that the compressor 1 is energized by the turbine 3. As described above, the gas turbine G1 and the rotating machine 4 constitute an electric power generator 50.

Because a concentration of fuel or burnable component in the operative gas G1 is less than its flammability limit and a temperature of the fuel is less than the minimum temperature needed for flaming combustion, the operative gas does not ignite due to the temperature increase at its compression by the compressor 1. The operative gas G1 may be added with high-concentration burnable gas to increase the fuel concentration.

The gas turbine GT further comprises a regenerator or heat exchanger 6 for heating the compressed gas G2 supplied from the compressor 1 to the catalytic combustor 2 by the use of gas G4 exhausted from the turbine 3 and a burner 7 for generating gas G5 to be used for heating the gas G4. Specifically, the burner 7 adds fuel to the gas 20 extracted from the compressor 1 and combusts the mixture to generate the heating gas G5 which is mixed in the exhaust gas G4 being supplied from the turbine 3 to the regenerator 6. The burner 7 is connected to an extraction control valve 8 for controlling an amount of the extracted gas G20 to be supplied to the burner 7. The gas G4 from the regenerator is supplied to the silencer not shown where noises are reduced therefrom and then exhausted into the atmosphere.

The flow rate control of the gas G20 to the burner 7 is performed by the extraction valve 8 in response to an output signal from the start control 21 of the controller 20 which controls the overall operation of the system which will be described below.

The flow rate control of the CMM from the CMM supply source 13 such as coal mines to the burner 7 is performed by a first fuel rate control valve 9 which is operated in response to a control signal from the start control 21 of the controller 20. The operative gas G1 is prepared by mixing the VAM from the VAM source 12 such as ventilation system of the coal mines with the CMM from the CMM source 13 as necessary while an amount of the CMM is controlled by a second fuel rate control valve 10. The CMM contains approximately 10-30% methane and the VAM contains less than 1% methane. The flow rate control of the CMM by the second fuel rate control valve 10 is performed in response to a signal from a load/stop control 22 in the controller 20. A purge air source 19 is connected to a passage extending from the VAM source 12 to the compressor 1 for a purge operation performed in the start-up process.

A first thermal sensor 31 is provided adjacent the inlet of the catalytic combustor 2 to detect a temperature of the gas entering into the catalytic combustor 2 and a second thermal sensor 32 is provided adjacent the catalytic combustor 2 to detect a temperature of the gas being discharged from the catalytic combustor 2. The inlet temperature obtained by the first thermal sensor 31 is transmitted as a first detected temperature signal into the start control 21 and the outlet temperature obtained by the second thermal sensor 32 is transmitted as a second detected temperature signal into the start control 21 and the load/stop control 22.

Besides, a third thermal sensor 33 is provided adjacent the outlet of the turbine 3 to detect a temperature of the gas being discharged from the turbine 3. The outlet temperature obtained by the third thermal sensor 33 is transmitted as a third detected temperature to the load/stop control 22 of the controller 20. A fourth thermal sensor 34 is provided adjacent the inlet of the regenerator 6 to detect a temperature of the gas entering into the regenerator 6. The inlet temperature obtained by the fourth thermal sensor is transmitted as a fourth detected temperature to the start control 21 of the controller 20.

The rotating shaft 5 connecting between the compressor 1 and the turbine 3, made of a single shaft member, is connected through a reducer 17 to the rotating machine 4. The rotating shaft 5 supports a rotation sensor 36 to detect the number of rotations of the rotating shaft 5 which is then transmitted to the load/stop control 22 of the controller 20.

A signal indicating the electric power energy generated by the rotating machine 4 is transmitted to the load/stop control 22 of the controller 20. A power conversion system 11 is provided so that the load/stop control 22 energizes the rotating machine 4 as a starter in the start-up operation.

As shown in FIG. 2, the turbine 3 and the regenerator 6 are connected to each other through an exhaust duct or passage 25. The exhaust passage 25 comprises a cylindrical portion 25 a adjacent the turbine and an expanding portion 25 b adjacent and expanding toward the regenerator 6, and the burner 7 is connected to the expanding portion 25 b in order to supply the heating gas G5 into the interior of the exhaust passage 25. The expanding structure of the expanding portion 25 b allows the heating gas G5 to be supplied evenly into the interior space of the large-scale regenerator 6, so that a heat exchange between the gasses G2 and G5 is accomplished while using the entire interior space of the regenerator 6.

As described above, the CMM from the CMM source (FIG. 1) is supplied to the burner 7. Also, an extracted gas passage 27 is branched from the passage 24 for supplying the compressed gas G2 from the compressor 1 to the regenerator 6, on which the burner 7 and the valve 8 are mounted.

The fundamental operations including start control, load control and stop control operations of the gas turbine GT will be described with reference to the FIG. 3 showing a start/stop time flow of the gas turbine. In this drawing, characteristic curves A to E represent the number of rotations of the rotating shaft of the gas turbine GT, the generated electric power, the open ratio of the first fuel rate control valve 9, the open ratio of the second fuel rate control valve 10 and the open ratio of the extraction valve 8, respectively.

First, discussions will be made to the start control operation. In this operation, upon receiving the start instruction, the start control 21 drives the power conversion system 11 in FIG. 1 to energize the rotating machine 4. Also, the valve 18 takes the open position. This causes that the gas turbine engine GT draws air to drive at a lower rotation number, for example, 20-30% of the rated speed (purge). Then, the valve 18 takes the open position, which causes that the gas turbine GT draws VAM from the VAM source 2 to increase the rotation number up to, for example, 60% of the rated speed in order to ignite the burner 7 in FIG. 1 for heating the regenerator 6 and also heating the interior of the catalytic combustor 2 up to a temperature necessary for the catalytic reaction. As shown in FIG. 3, the extraction valve 8 is opened gradually after the completion of the purge operation. The open ratio of the valve 8 is kept constant after the ignition of the burner 7. Then, the second fuel flow rate control valve 10 is opened by the control signal from the load/stop control during the catalytic combustion within the catalytic combustor 2 in FIG. 1 to initiate the supply of CMM from the CMM source 13 to the compressor 1 (CMM supplied). Then, the combustion of the burner 7 is controlled to prevent a temperature increase at the inlet of the catalytic combustor 2 which would otherwise be caused by the supply of the CMM.

For example, as shown in FIG. 3 this combustion control is conducted by gradually decreasing the open ratios E and C of the extraction valve 8 and the first fuel flow rate control valve 9 and the resultant amounts of the gases G20 and CMM supplied to the burner 7. The inlet temperature of the catalytic combustor 2 is detected by the thermal sensor 31 and the signal indicating the detected temperature is transmitted to the start control 12 of the controller 20. Upon receiving the signal, the start control 21 transmits control signals to the extraction valve 8 and the first fuel flow rate control valve 9 to control their open ratios E and C, respectively. As shown in FIG. 3, when the generated electric power B exceeds zero kW, i.e., the electric power generation is initiated, the open ratios E and C of the extraction valve 8 and the first fuel flow rate control valve 9 are reduced to zero to halt the supply of the extracted gas G20 and the CMM to the burner 7 and thereby turn off the burner flame.

Next, the discussions will be made to the load control. As shown in FIG. 3, once the electric power generation is initiated, the open ratio D of the second fuel flow rate control valve 10 is increased in response to the control signal from the load/stop control 22, which increases the amount of CMM to be supplied from the CMM source 13 to the compressor 1. Also, after the burner 7 is completely turned off, the catalytic combustor 2 continues its catalytic combustion. Further, as shown in FIG. 3, the open ratio D of the second fuel flow rate control valve 10 is gradually increased to increase the amount of CMM to be supplied to the compressor 1 until the engine's rotation number A reaches the rated number (100%) to generate the rated electric power B (rated load). When the load reaches the rated load, the concentration of CMM in the operative gas G1 is controlled by controlling the amount of CMM to be supplied to the compressor 1 by the use of second fuel flow rate control valve 10 in FIG. 1.

In the stop control, upon receipt of the stop signal, as shown in FIG. 3 the start control 21 drives to gradually decrease the electric power B to be generated and also the open ratio D of the second fuel flow rate control valve 10 to decrease the amount of CMM to be supplied to the catalytic combustor 2, which reduces engine's rotation number A and the generating electric power down to zero (no-load). This condition is maintained for a certain period of time during which the engine as a whole is cooled down (aftercooling). After the engine is cooled down sufficiently, the second fuel flow rate control valve 10 is completely closed to de-energize the gas turbine GT, which in turn brings the gas turbine GT into a free-running condition.

The burner 7 drives not only when starting the engine but also when any combustion trouble occurs at the catalytic combustor 2. For example, when the outlet temperature of the catalytic combustor detected by the second thermal sensor 32 decreases less than the predetermined temperature, it is determined that any combustion trouble has occurred due to, for example, deterioration of the catalyst and, as a result, the controller 20 drives to open the extraction valve 9 and the first fuel flow rate control valve 9 and ignites the burner 8. This increases the temperature of the exhaust gas G4 entering the regenerator 6 and also the compressed gas G2 to be supplied to the catalytic combustor 2, which energizes the catalytic combustor 3 sufficiently to prevent any drop in output of the engine.

According to the embodiments, the gas turbine can be driven smoothly. Specifically, the temperature of the exhaust gas G4 from the turbine 3 in the staring operation of the engine is low and therefore the catalytic combustor 2 is unlikely to be well activated, which makes it difficult to supply high-pressure and high-temperature compressed gas to the turbine and to increase the rotation smoothly. According to the embodiment, however, the burner 7 is driven at the start-up operation of the engine to increase the temperature of the exhaust gas G4 entering the regenerator 6. This ensures that by the heat exchange at the regenerator 6 the temperature of the compressed gas G2 to be supplied to the catalytic combustor 2 is heated, which activates the catalytic combustor effectively to ensure a smooth starting of the engine.

Also, because the heating burner 7 is provided outside the exhaust gas passage 25 rather than the inside the passage 25, no loss in pressure loss or in output energy occurs in the exhaust passage or no output decrease occurs, which ensures an efficient driving of the gas turbine GT. Further, because the heating burner is not provided within the exhaust passage 25, the passage can be smaller in size, which results in a compact gas turbine GT.

Furthermore, the extraction valve 8 is provided on the upstream side of the heating burner 7 to continuously increase or decrease the amount of extracted gas G20 to be supplied to the burner 7. This ensures that the amounts of the extracted gas G20 and the fuel to be supplied to the burner 7 are suitably controlled in response to the rotation number of the engine, which in turn ensures to control the flow rate and the temperature of the heating gas G5 from the burner 7 and thereby to control the inlet temperature of the catalytic combustor 2.

When the engine works under the non-rated operation, an amount of operative gas passing through the gas turbine is less than that under the rated operation. This results in that the heating burner 7 requires less fuel, which in turn means that the burner 7 can be smaller in size.

Although the CMM and the VAM are used as operative gases in the above-described embodiments, another gas in which a concentration of burnable component therein is less than its flammability limit can be used instead.

Although preferred embodiments of the invention have been described with reference to the accompanying drawings, various modifications can be made without departing from the gist of the invention and they are within the scope of the invention.

PARTS LIST

-   1: compressor -   2: catalytic combustor -   3: turbine -   4: generator -   6: regenerator -   7: heating burner -   8: extraction valve -   25: exhaust gas passage -   G1: operative gas -   G2: compressed gas -   G3: combustion gas -   G4: exhaust gas -   G5: heating gas -   G20: extracted gas 

1. A lean-fuel gas turbine engine, comprising: a compressor for compressing an operative gas to generate a compressed gas, the operative gas having a concentration of burnable component which is less than a flammability limit thereof; a catalytic combustor for combusting the compressed gas by a catalytic reaction with an aid of a catalyst accommodated therein to generate a combustion gas; a turbine adapted to be driven by the combustion gas supplied from the catalytic combustor; a regenerator for heating the compressed gas supplied from the compressor to the catalytic combustor by an exhaust gas supplied from the turbine through an exhaust gas passage to the regenerator; a burner for burning a gas extracted from the compressor with a fuel to generate a heating gas and supplying the heating gas into the exhaust gas passage; and a valve for controlling an amount of the extracted gas to be supplied to the burner.
 2. The lean-fuel gas turbine engine of claim 1, wherein the valve is adapted to continuously increase or decrease the amount of the extracted gas to be supplied to the heating burner.
 3. The lean-fuel gas turbine engine of claim 1, wherein the heating burner is activated in a start-up operation of the gas turbine engine.
 4. The lean-fuel gas turbine engine of claim 3, wherein the heating burner works in a condition where the gas turbine engine works under the non-rated operation of which a rotation number is less than that of a rated operation of the gas turbine engine.
 5. The lean-fuel gas turbine engine in any one of claim 1, wherein the heating burner works when a combustion failure occurs at the catalytic combustor. 